1. Field of the Invention
Embodiments of the present invention are directed in general to the fluorescence of alkaline-earth based, aluminum-silicate phosphors doped with trivalent metals, and configured to emit in the orange to red region of the spectrum. Such phosphors may be used in white light illumination systems commonly called “white light emitting diodes” (LEDs).
2. Description of the Related Art
Devices commonly known as “white LEDs” are known in the art, and they are relatively recent innovations. It was not until light emitting diodes emitting in the blue/ultraviolet region of the electromagnetic spectrum were developed that it became possible to fabricate a white light illumination source based on an LED. Economically, white LEDs have the potential to replace incandescent light sources (light bulbs), particularly as production costs fall and the technology develops further. In particular, the potential of a white light LED is believed to be superior to that of an incandescent bulb in lifetime, robustness, and efficiency. For example, white light illumination sources based on LEDs are expected to meet industry standards for operation lifetimes of 100,000 hours, and efficiencies of 80 to 90 percent. High brightness LEDs have already made a substantial impact on such areas of society as traffic light signals, replacing incandescent bulbs, and so it is not surprising that they will soon provide generalized lighting requirements in homes and businesses, as well as other everyday applications.
There are several general approaches to making a white light illumination system based on light emitting phosphors. To date, most white LED commercial products are fabricated based on the approach shown in FIG. 1, where light from a radiation source affects the color output of the white light illumination. Referring to system 10 of FIG. 1, a radiation source 11 (which may be an LED) emits light 12, 15 in the visible portion of the electromagnetic spectrum. Light 12 and 15 is the same light, but is shown as two separate beams for illustrative purposes. A portion of the light emitted from radiation source 11, light 12, excites a phosphor 13, which is a photoluminescent material capable of emitting light 14 after absorbing energy from the source 11. The light 14 can be a substantially monochromatic color in the yellow region of the spectrum, or it can be a combination of green and red, green and yellow, or yellow and red, etc. Radiation source 11 also emits blue light in the visible that is not absorbed by the phosphor 13; this is the visible blue light 15 shown in FIG. 1. The visible blue light 15 mixes with the yellow light 14 to provide the desired white illumination 16 shown in FIG. 1.
What is needed in the art is an enhancement to the silicate-based, orange-red phosphors of the prior art where the enhancement is manifested at least in part by an equal or greater conversion efficiency of blue light to orange light, a so-called red shift. The enhanced orange-red phosphor with low gravity density and low cost may be used in conjunction with a blue LED to generate light whose color output is stable, and whose color mixing results in the desired uniform, low color temperature and warm white color rendering index.